Structural analogs of the peptide hormone, angiotensin-II, are being prepared by solid phase synthesis for biological evaluation. Amino acid side chains are being altered in a systematic fashion by the synthesis and incorporation of unnatural amino acids into the peptide chain. Increase in blood pressure in the nephrectomized, ganglion-blocked rat is the primary test for agonist and antagonistic activity. Conformational studies using nuclear magnetic resonance, optical rotatory dispersion and circular dichroism spectroscopy, are carried out on selected analogs. Attempts are made to obtain suitable crystals for X-ray diffraction studies.